Electro-active lenses can be made by several methods, including patterning a series of concentric electrodes of conductive material on a first substrate, then sandwiching a layer of liquid crystal between the first substrate and second substrate opposite the first substrate. The second substrate may have one or more circular patterns of conductive material patterned on it, or any other shape to match or exceed the area of the patterned electrodes, allowing an electrical circuit to be formed that creates a voltage field between the two substrates. When an electrical field is applied across the electrodes, the liquid crystal material between the two substrates changes its index of refraction.
By applying a gradient of voltage fields at different electrode locations on the lens, a gradient of index of refraction may be created, creating a lens. The higher the number of electrodes that are used, the finer the resolution of gradient of refractive index can be created. This results in a smoother wavefront curvature, and hence provides a better quality optic.
However, increasing the number the electrodes also increases the complexity of the electronics as well as the light-blocking elements that supply power to the electrodes, so methods have been developed to allow a small number of power supply lines to apply a voltage gradient across a larger number of electrodes. In particular, N power supply lines can be used to apply a voltage gradient across M>N electrodes with resistive bridges between the electrodes. In these electro-active lenses, every M/Nth electrode is connected to a power supply line, and the other electrodes are coupled to each other with resistive bridges.
In conventional electro-active lenses with resistive bridges, the resistive bridges are made in such a manner that the electrode ring is no longer continuous, degrading optical quality. The problem can be partially solved by fabricating the resistive bridges in the same plane as the electrodes, locating the resistors in between adjacent electrodes. In some cases, there are additional shortcomings, including the use of extremely high resistive materials, which are difficult to manufacture in a controllable manner, and the need to fill the entire gap between electrodes with resistive material is required to fill a large area. In general, it is desirable to reduce the gap between electrodes to improve optical performance, but this can exacerbate the difficulty of manufacturing the resistive components.